﻿PROSOBRANCHIATA. 



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The present species much resembles P. innexa, with which, in fact, at first sight, 

 it may be easily confounded ; on a closer inspection, however, differences will be 

 detected which render it impossible to regard it as even a strongly-marked 

 variety of P. innexa. In the general form, P. constricta is a slenderer shell, with a 

 more pointed spire, and, instead of the shallow, obscure furrow, bordered by a row 

 of granulations which runs round the posterior margins of the whorls in P. innexa, 

 the present species presents a wide, conspicuous channel, defined by a sharp, elevated 

 ridge ; the outer lip is much less arched, and is not thickened or plicated within, 

 and the sinus is deep, narrow, three-cornered, and placed in the front part of the 

 margin, instead of the wide, rounded sinus extending over the whole width of the 

 margin which characterises P. innexa. 



Size. — Axis, rather more than 8-12ths of an inch; diameter, 3-12ths of an inch. 



Localities. — Barton, Highcliff, Highgate. 



No. 179. Pleurotoma pyrgota. F. E. Edwards. Tab. XXVIII, fig. 16, a—c. 



P. testa sub-fusiformi, turritd, longitudinal iter obscure costulatd, concentrice sulcata: 

 anfractibus ad humeros carinatis, antice planulatis, sub-conicis, postice canaliculatis, 

 transversim lineatis, crenato-marginatis ; costellis antice bifurcatis, sub-obsoletis : aperturd 

 oblongo-ovali, in canali brevi exeunti ; labro intus plicifero ; sinu lato, sub-semicirailari, in 

 rnargine collocato. 



Var. a. Testa costellis distinctioribus, productioribus : anfractibus antice granoso- 

 lineatis, cceterum Icevibus. 



Shell sub-fusiform, turreted, longitudinally ribbed, and concentrically furrowed : 

 the spire, which consists of seven or eight volutions, exclusive of the smooth, conical 

 pullus, is moderately elevated, forming about one half of the entire shell ; the whorls 

 flat-sided, giving a nearly conical aspect to the anterior part of the shell, sharply 

 carinated at the shoulders, and having the posterior margins channelled and bordered 

 round the suture by a sharp, elevated line, simple or feebly crenulated, the concave 

 space between which and the shoulder is smooth ; the keel on the shoulders is 

 notched with much regularity, presenting a row of oblong, somewhat oblique, rib-like 

 tubercles. These tubercles are prolonged anteriorly, and bifurcate, forming two 

 curved, narrow, obscure ribs, which are lost as they cross the middle of the whorls ; 

 the concentric furrows are shallow and wide, the intervening spaces becoming 

 gradually more elevated and sharper as they approach the base of the shell. The 

 aperture is of a narrow, elongated, oval form, and terminates in front in a short, wide 

 canal ; the outer lip is slightly arched, somewhat thickened and plicated within ; 

 and the sinus, which extends over the whole margin, is wide and deep, and nearly 

 semicircular. 



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